Every other Numberblock from Twenty-One to Ninety-Nine appear as compound Numberblocks.
Zero meets One, who is excited to show off that she can count higher than ever before. She showcases her row of 10 by 10 springs, with flippers for each 10 interval. Then One throws a mystery present to the last flipper, and begins to count up using the magic mirror that can copy one of her to a spring and add with the last number, while she rides her scooter.
After a lot of counting, Ninety-Nine is at the last flipper. One then jumps up, which adds to... yep, One Hundred. She then jumps down using the parachute that was in the mystery present, and splits up into a hundred ones with a hundred parachutes flying down to ground.
All the Numberblocks from 0-100 appear in this episode.
Every number after 20 (excluding the Numberblocks that are multiples of ten) is shown as a compound Numberblock despite the fact that 21, 22, and 25 have already been figured-out before this episode.
This was probably because they wanted consistency instead of a "figured-out, figured-out, compound, compound, figured-out, compound" situation.
After 100 split up, we see 100 ones at the same time. Which is a Numberland record, beating Hiccups that had 40 ones.
When 8 is counting up, he has 4 limbs which happens in some episodes.